Heretofore, component measuring devices have been used to detect a biological component contained in a body fluid such as blood or urine and optically measure the amount and properties of the detected biological component. For example, Japanese Laid-Open Patent Publication No. 09-145614 discloses a diffused light reflection reading pad as a device for detecting glucose in blood. Specifically, when a reagent test pad that has been colored by blood is irradiated with light (irradiation light) from an irradiating means, the reagent test pad reflects the light, which is applied to a light sensor to detect glucose in the blood.